Field of the Invention
The present invention relates generally to memory cards, and more particularly to a memory card (e.g., a multi-media card (MMC)) wherein a two-step mold procedure is used to form an outer memory card body which encapsulates an inner memory card body and leadframe structure so that remaining portions of the tie bars used to connect the external signal contacts of the leadframe to the outer frame thereof can be effectively covered by the outer memory card body. The outer body of the memory card of the present invention may also be configured such that the host socket connector pins of a host socket are not damaged by the repeated advancement of the memory card into the host socket.
As is well known in the electronics industry, memory cards are being used in increasing numbers to provide memory storage and other electronic functions for devices such as digital cameras, MP3 players, cellular phones, and personal digital assistants. In this regard, memory cards are provided in various formats, including multi-media cards and secure digital cards.
Typically, memory cards comprise multiple integrated circuit devices or semiconductor dies. The dies are interconnected using a circuit board substrate which adds to the weight, thickness, stiffness and complexity of the card. Memory cards also include electrical contacts for providing an external interface to an insertion point or socket. These electrical contacts are typically exposed on the backside of the circuit board substrate, with the electrical connection to the dies being provided by vias which extend through the circuit board substrate.
In an effort to simplify the process steps needed to fabricate the memory card, there has been developed by Applicant a memory card wherein a leadframe assembly is used an alternative to the circuit board substrate, as described in Applicant's co-pending U.S. application Ser. No. 09/956,190 entitled LEAD-FRAME METHOD AND ASSEMBLY FOR INTERCONNECTING CIRCUITS WITHIN A CIRCUIT MODULE filed Sep. 19, 2001, the disclosure of which is incorporated herein by reference. As is described in Ser. No. 09/956,190, the leadframe and semiconductor die of the memory card are covered with an encapsulant which hardens into a cover or body of the memory card. The body is sized and configured to meet or achieve a “form factor” for the memory card. In the completed memory card, the contacts of the leadframe are exposed within a common surface of the body, with the die pad of the leadframe and the semiconductor die mounted thereto being disposed within or covered by the body.
Memory cards, such as multi-media cards, are used by advancing the same into a host socket which includes a plurality of connector pins. Many host sockets include nine connector pins to accommodate the seven contacts included in many memory card formats such as multi-media cards, and the nine contacts included in the secure digital card memory card format. One of the drawbacks associated with leadframe based memory cards is that portions of the tie bars which are used to connect the contacts to the outer frame of the leadframe are typically exposed in the leading edge of the memory card which is initially advanced into the host socket. More particularly, exposed within this leading edge are the severed ends of the tie bars created as a result of the cutting or singulation process typically used to separate the outer frame of the leadframe from the remainder thereof subsequent to the formation of the body of the memory card. These exposed portions of the tie bars give rise to a potential short against the metal features of the host socket, and are thus highly undesirable. As a result, despite the reduced costs associated with leadframe based memory cards, certain manufacturers are reluctant to use the same due to the potential of generating electrical shorts as described above, and further in view of the appearance of the memory card attributable to the exposure of the severed ends of the tie bars in the leading edge thereof.
Another drawback associated with currently known leadframe based memory cards is their susceptibility to extreme warpage. In this regard, the memory card has a relatively large area, with the thermal expansion coefficients of the memory card body, the leadframe, and the semiconductor die or other internal circuit elements differing from each other. As the capacity of the memory increases, the memory card frequently emits a large amount of heat or receives heat from the device in which it is used. This heat may cause warpage of the memory card, which deteriorates the reliability thereof and may result in the cracking of the internal leadframe or electronic circuit elements.
Yet another deficiency of currently known leadframe based memory cards is that the leading edge of the body thereof is typically fabricated to define a corner which is angled at approximately ninety degrees. This sharp corner, provided on a body typically fabricated from a material significantly harder than general plastic products, often results in some measure of damage to the device into which the memory card is inserted. Such damage is typically evident over time after repeated cycles of the insertion of the memory card into the host socket of the device, the damage often occurring as a result of the contact or rubbing of the sharp leading edge of the memory card against the device.
The present invention addresses and overcomes the above-described deficiencies of currently known leadframe based memory cards by providing a memory card wherein a two-step mold procedure is used to form an outer memory card body which partially encapsulates an inner memory card body itself partially encapsulating the memory card leadframe structure. As a result, the remaining portions of the tie bars used to secure the contacts to the outer frame of the leadframe are completely covered by the outer memory card body. The outer memory card body may further be formed to define a rounded or chamfered leading edge adapted to prevent damage to any device including a host socket into which the memory card is advanced. Also alleviated by the configuration of the memory card of the present invention are many of the warpage problems discussed above. These and other attributes of the present invention will be described in more detail below.